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FLIGHT INSTRUCTOR'S MANUAL   139

the process is actually a series of comparisons and estimations with intermediate objects until the final result is reached. This is usually done without any realization of how the result is reached, and the factors involved should be called to the student's attention. He should then attempt to perfect his judgment of distance by practice in the estimation of distance on the ground, as well as in the air. 
  In estimating altitude, a similar procedure is followed except that there are no intermediate objects. The distance is in a vertical plane instead of the horizontal and the airplane is in movement, all of which add to the difficulty of the novice in arriving at an estimate of any accuracy.
  However, with experience and practice, altitudes up to a thousand feet can be estimated with fair accuracy, although above this point the appearance of elevation of an object decreases and all features tend to merge into the background, with their outlines becoming indistinct. This makes their relative size difficult to judge. Therefore, the only aid in perfecting the ability to judge above this altitude is through noting the reading of the altimeter and associating it with the general appearance of the earth and such features as are more readily distinguishable. This, of course, will require that it be done when the altimeter registers that actual height above the ground, and is difficult in rolling or mountainous country. 
  The judgment of altitude in feet, hundreds of feet, or thousands of feet, is not nearly so important as the ability to estimate the amount of maneuvering that can be done from any given altitude. This ability can only be developed by actual practice in maneuvering from predetermined altitudes and this practice continued until the student thinks of altitude as a maneuvering space, rather than a distance in feet. 
  The ability to estimate the distance the airplane will glide to a landing is the real basis of all power-off accuracy work. This will largely determine the amount of maneuvering that can be done from any altitude, since one is a factor of the other. This ability is only attained through experience and practice with the proper factors being brought to the student's attention as it is gained. 
  The first requisite to judging gliding distance is the ability to maintain a constant gliding speed and the ability to recognize a "normal glide." The normal glide is considered to be the most efficient, being the angle and speed at which the airplane will go the greatest linear distance for the altitude to be utilized. If an uneven glide is allowed, the student will have no way of knowing or of ever learning the actual effects of the wind, and he will be unable to distinguish between effects of the varying glide and the effects of the wind, which is often variable enough to cause considerable trouble. This will destroy any developing judgment of the room for, or effects of, maneuvering, and will also leave the student with no sound basis for judging the gliding characteristics of a strange airplane. 
  The speed range of the airplane will introduce the factor of the distance covered while the normal glide is being established. With modern, well-streamlined airplanes of wide speed range, allowance must be made for the distance covered after the throttle is closed 
    
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